Greenhouse effect: In the laboratory

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As well as taking measurements in the Earth’s atmosphere, scientists have also investigated some components of the greenhouse effect in the laboratory. Scientific instruments can measure how much energy is absorbed at certain frequencies by different gases. Professor Frank James explains John Tyndall’s early climate experimentsin the 1850s. Tyndall declared that without greenhouse gases (such as water vapour and carbon dioxide) the Earth would be ‘held fast in the iron grip of frost’.

Just as visible light comes in all the colours of the rainbow, the infrared heat energy given off by the Earth comes in different shades, or frequencies. Different gases absorb different frequencies. Over a hundred years ago, scientists devised instruments called spectrometers to measure the absorption properties of atmospheric gases. Spectrometers used today have much greater precision and can measure a broader range of frequencies. By examining these measurements, scientists discovered that oxygen and nitrogen – the most abundant atmospheric gases – don’t absorb infrared energy. But gases such as water vapour, carbon dioxide and methane each absorb a distinctive set of infrared frequencies, making them efficient greenhouse gases.

Scientists carry out laboratory experiments in which they focus an infrared heat source on one end of a tube filled with the gas they wish to study. A spectrometer at the other end of the tube measures in detail the amount of infrared energy passing through. The amount of energy not escaping from the tube will have been absorbed by the gas under examination. This enables scientists to determine not only which gases are capable of absorbing infrared heat energy, but also how much of the energy each gas absorbs. Measurements show that of the three main greenhouse gases, molecule for molecule, methane is the strongest, followed by carbon dioxide and then water vapour.

Joseph Fourier was a mathematician fascinated by heat. At the beginning of the 19th century he developed mathematical techniques to investigate heat transfer. As part of his research he mapped out all the factors that affect the Earth’s heat energy balance. He suggested that the atmosphere could regulate our planet’s surface temperature by preventing heat energy, also known as infrared energy, from escaping to space. He anticipated the role of what we now call the greenhouse effect in controlling the climate, but did not fully explain its mechanisms. His ideas were developed further by John Tyndall and Svante Arrhenius.

In 1859, John Tyndall was the first to find evidence at a molecular level of the greenhouse effect. He was interested in explaining ice ages and believed the answer might be found in the atmosphere’s composition. He designed an apparatus to show that small amounts of ‘perfectly colourless and invisible gases and vapour’ found in the atmosphere – such as water vapour, carbon dioxide and methane – can absorb infrared heat energy. He suggested that these gases, now called greenhouse gases, play a significant role in controlling the planet’s climate.

Like John Tyndall, Svante Arrhenius, a chemist, was interested in finding out the cause of ice ages. In 1896 he published a paper that examined the effect of carbon dioxide concentration in the atmosphere on the surface temperature of the Earth. He predicted that any doubling of the percentage of carbon dioxide in the air would raise the temperature of the Earth’s surface by 5 to 6 °C. In 1908 he adjusted his model and calculated that average surface temperatures would increase by 4 °C for a doubling of carbon dioxide. These results are close to current estimates, despite the relatively rudimentary information Arrhenius’ model was based upon.

During the first half of the 20th century, Guy Callendar, a British steam engineer, set out to investigate, at home during his spare time, the influence of human activity on the greenhouse effect using his own weather station, world weather records, measurements of carbon dioxide and calculations. In 1938 he suggested that rising global temperatures and rising atmospheric carbon dioxide levels owing to increased coal burning and human activity are closely linked. His work is seen by many as the starting point of modern climate science and it had a significant influence on scientists who investigated the greenhouse effect further.

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There are many institutions and organisations around the world researching climate science, how our climate is changing, and ways of responding. Here are just a few…

British Antarctic Survey (BAS)

Department for the Environment, Food and Rural Affairs (Defra)

Department of Energy and Climate Change (DECC)

Energy Saving Trust (EST)

Environmental Change Institute (ECI)

European Space Agency (ESA)

The Geological Society (GS)

Grantham Institute for Climate Change (GICC)

Intergovernmental Panel on Climate Change (IPCC)

Met Office (MO)

National Academy of Sciences (NAS)

National Aeronautics and Space Administration (NASA)

National Oceanic and Atmospheric Administration (NOAA)

National Oceanography Centre (NOC)

The Royal Society (RS)

Tyndall Centre for Climate Change Research (TCCCR)

UK Climate Impacts Programme (UKCIP)

United Nations Framework Convention on Climate Change (UNFCCC)

World Climate Research Programme (WCRP)

World Meteorological Organization (WMO)

Greenhouse effect

A natural process in the atmosphere whereby greenhouse gases trap heat near the Earth’s surface. This keeps the Earth’s surface temperature roughly 30 °C warmer than it would otherwise be. Changing the amount of greenhouse gases in the atmosphere changes the strength of the greenhouse effect, which in turn changes the temperature of the atmosphere near the Earth’s surface.

Climate

A summary of the weather in a particular region over a period of at least ten years, but more commonly defined over 20 - 30 years. The climate describes both the average weather conditions (for example temperature, rain, snow and wind) in a particular region as well as the extremes.

Water vapour

Water in the form of a gas. Water vapour is the most common greenhouse gas.

Carbon dioxide

An important greenhouse gas, with the chemical formula CO2. After water vapour, carbon dioxide is the biggest contributor to the greenhouse effect.

Visible light

Energy of a specific frequency range that can be detected by the human eye.

Spectrometer

A device used to measure the frequency and intensity of waves of energy, which can inform scientists about the properties of the material the energy came from or passed through. Scientists use spectrometers on satellites to measure the amount of ozone in the atmosphere.

Infrared energy

Methane

A greenhouse gas about 25 times more powerful than carbon dioxide. Methane contains carbon and is one of the gases exchanged in the carbon cycle.

Energy balance

The difference between the total energy reaching the Earth from the Sun and the total energy emitted by the Earth into space. Also known as the energy budget.

Averaged over geological periods of time, the difference is zero. Over short periods of time, when the difference is not zero, the Earth’s surface temperature will change. For example, when the amount of energy reaching the Earth exceeds the amount lost into space, the temperature of land, atmosphere and ocean will increase.

Ice age

A period of time during which the Earth’s average temperature is reduced. Polar ice caps and glaciers grow in size and global sea levels fall dramatically. The world began to emerge from the last ice age about 22,000 years ago and reached the current warm conditions about 12,000 years ago.